Masonry Magazine October 1995 Page. 40
Centering is typically provided by wood construction. An example of centering for an arch is shown in Fig. 11. Careful construction of the centering will ensure a more pleasing arch appearance and avoid layout problems, such as an uneven number of brick to either side of the keystone.
Immediately after placement of the keystone, very slight downward displacement of the centering, termed easing, can be performed to cause the arch voussoirs to press against one another and compress the mortar joints between them. Easing helps to avoid separation cracks in the arch. In no case should centering be removed until it is certain that the masonry is capable of carrying all imposed loads. Premature removal of the centering may result in collapse of the arch.
Centering should remain in place for at least seven days after construction of the arch. Longer curing periods may be required when the arch is constructed in cold weather conditions and when required for structural reasons. The arch loading and the structural resistance of the arch will depend upon the amount of brickwork surrounding the arch, particularly the brick masonry within spandrel areas. Appropriate time of removal of centering for a structural arch should be determined with consideration of the assumptions made in the structural analysis of the arch. It may be necessary to wait until the brickwork above the arch has also cured before removing the centering.
Workmanship
All mortar joints should be completely filled, especially in a structural member such as an arch. If hollow brick are used to form the arch, it is very important that all face shells and end webs are completely filled with mortar. Brick masonry arches are sometimes constructed with the units laid in a soldier orientation. It may be difficult to lay units in a soldier position and also obtain completely filled mortar joints. This is especially true for an arch with tapered mortar joints. In such cases, the use of two or more rings of arch brick laid in rowlock orientation can help ensure full mortar joints.
SUMMARY
This Technical Notes is an introduction to brick masonry arches. A glossary of arch terms has been provided. Many different types of brick masonry arches are described and illustrated. Proper detailing of brick masonry arches for appearance, structural support and weather resistance is discussed. Material selection and proper construction practices are explained. Other Technical Notes in this Series discuss the structural design of arches.
The information and suggestions contained in this Technical Notes are based on the available data and the experience of the engineering staff of the Brick Institute of America. The information contained herein must be used in conjunction with good technical judgment and a basic understanding of the properties of brick masonry. Final decisions on the use of the information contained in this Technical Notes are not within the purview of the Brick Institute of America and must rest with the project architect, engineer and owner.
REFERENCES
1. Brickwork Arch Detailing, Ibstock Building Products, Butterworth & Co. (Publishers) Ltd., London, England, 1989, 114 pp.
2. Lynch, G., Gauged Brickwork, A Technical Handbook, Gower Publishing Company, Aldershot, Hants, England, 1990, 115 pp.
3. Trimble, B.E., and Borchelt, J.G., "Jack Arches in Masonry Construction," The Construction Specifier, Construction Specifications Institute, Alexandria, VA, January 1991, pp. 62-65.
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40 MASONRY-SEPTEMBER/OCTOBER, 1995